Sleep Calculator

How to use

1. 1Pick a mode at the top: Wake up at to plan bedtime around a fixed alarm, or Go to bed at to plan wake time around a fixed bedtime. Use Sleep now to pre-fill the current time when you want to sleep right away.
2. 2Enter a target time in the time input. The display below switches between 12-hour (AM/PM) and 24-hour formats; the input always uses 24-hour for clarity.
3. 3Read the result panel: each row is one option, with the recommended four-to-six cycle range highlighted in green. Each row shows the time, how many cycles it covers, and how long that is in hours and minutes.
4. 4Optional: open Advanced and adjust Sleep cycle length (default 90 minutes) or Time to fall asleep (default 14 minutes) if you have a calibrated estimate from a sleep tracker.
5. 5Use Copy schedule to put the full plan on your clipboard, ready to paste into a calendar event, an alarm app, or a note for later.

About this tool

Sleep Calculator plans bedtime and wake-up time around full sleep cycles, so you wake when sleep is naturally lightest instead of mid-cycle. Adult sleep moves through repeating cycles of light sleep, deep sleep, and REM, averaging about 90 minutes from start to finish, and the most common research-backed recommendation for waking up rested is to wake at the end of a cycle rather than partway through one. Pick a mode at the top: Wake up at lets you set a target alarm time and returns the bedtimes that line up with the end of each cycle, while Go to bed at lets you set a bedtime (or hit Sleep now to use the current local time) and returns the wake times that line up with each cycle. The output shows six options stacked from one cycle up to six cycles, with the four-to-six cycle range marked Recommended (about six to nine hours of sleep, which covers the typical adult sleep need). Each row shows the actual time, how many cycles it corresponds to, the total duration of sleep, and a marker if the result lands on a different calendar day, so a 4 AM bedtime that turns into a wake-up the next afternoon is never ambiguous. Two advanced controls fine-tune the math: Sleep cycle length adjusts the cycle duration from 60 to 120 minutes (the average is 90, but most adults run somewhere in between, and your own number can be calibrated against a sleep tracker), and Time to fall asleep adds a buffer (default 14 minutes, the typical sleep-onset latency) so the schedule reflects when you actually start sleeping rather than when you get into bed. A 12-hour or 24-hour display toggle keeps the output readable in any region. A Copy schedule button puts the full plan on the clipboard as plain text ready to paste into a notes app, a calendar event, or a message to a partner who needs to set the same alarm. Useful for shift workers planning a recovery nap, parents choosing a child's bedtime, students timing study and rest, athletes lining up training and recovery, travelers shifting schedule for a flight, and anyone who has wondered whether to push through one more cycle or wake an hour earlier and feel better. All math runs locally on your device, so nothing about your sleep schedule is uploaded.

Free to use. Works in your browser. No signup, no login.